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Impression Materials

Impression Materials. Objectives. Introduction Ideal properties Classification Indications Hydrocolloids Non-elastic. Agar Alginate. Plaster Impression compound Zinc oxide eugenol waxes. Introduction.

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Impression Materials

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  1. Impression Materials

  2. Objectives • Introduction • Ideal properties • Classification • Indications • Hydrocolloids • Non-elastic Agar Alginate Plaster Impression compound Zinc oxide eugenol waxes

  3. Introduction • Impression materials are used to record the shape of the teeth and alveolar ridges. • Materials in common use can be classified as elastic or non-elastic according to the ability of the set material to be withdrawn over undercuts.

  4. Ideal Properties of Impression Materials • (1) Non toxic and non irritant • (2) Acceptability to the patient: • (a)Setting time, (b)Taste, (c)Consistency • (3) Accuracy : • (a) Surface reproducibility • (b) Dimensional stability • 4) Use of material : (a) Ease of mixing (b) Working time (c) Setting time (5) Compatible with model materials (6) Economics of material (a) Cheap (b) Long shelf life (c) Accuracy (save redoing impression)

  5. Plaster Compound Waxes ZnO - Eugenol Polysulfide Silicones Polyether CLASSIFCATION Non-elastic Impression Materials Agar (reversible) Aqueous Hydrocolloids Alginate (irreversible) Elastic Condensation Non-aqueous Elastomers Addition

  6. Indications • Diagnostic casts • Indirect reconstruction of prosthesis • Bite registration

  7. Aqueous Hydrocolloids Elastic • Agar • Alginate

  8. Aqueous Hydrocolloids • Colloidal suspensions • chains align to form fibrils • traps water in interstices • Two forms • sol • viscous liquid • gel • elastic solid • Placed intra-orally as sol • converts to gel by thermal or chemical process

  9. Aqueous HydrocolloidsDisadvntages • Semi-permeable membranes • poor dimensional stability • Evaporation – dry • Syneresis • fibril cross linking continues • contracts with time • exudes water • Imbibition • water absorption • swells

  10. Reversible Hydrocolloid (Agar) • Indications • crown and bridge • high accuracy

  11. heat to 70-100 0C agar hydrocolloid (hot) agar hydrocolloid (cold) (sol) (gel) cool to 37-50 0C Composition • Agar • complex polysaccharide • gelling agent • Borax • strength • Potassium sulfate • (improves gypsum surface ) • Water (more than 8O%)

  12. Manipulation • Gel in tubes • Syringe • and tray material

  13. Manipulation • 3 chamber conditioning unit • (1) liquefy at 100°C for 10 minutes • converts gel to sol • (2) store at 65°C • place in tray • (3) temper at 45°C for 3 minutes • seat tray • Place into patients mouth O’Brien Dental Materials & their Selection 1997

  14. Advantages Disadvantages • Dimensionally accurate • Hydrophilic • displace moisture, blood, fluids • Inexpensive • after initial equipment • No custom tray or adhesives • Pleasant • No mixing required • Initial expense • special equipment • Material prepared in advanced • Tears easily • Dimensionally unstable • immediate pour • single cast • Difficult to disinfect Phillip’s Science of Dental Materials 1996

  15. Irreversible Hydrocolloid (Alginate) • Most widely used impression material • Indications • study models • removable fixed partial dentures

  16. 2 Na3PO4 + 3 CaSO4 Ca3(PO4)2 + 3 Na2SO4 H2O Na alginate + CaSO4 Ca alginate + Na2SO4 (powder) (gel) Composition • Sodium alginate • salt of alginic acid • mucous extraction of seaweed (algae) • Calcium sulfate • reactor • Sodium phosphate • retarder • Filler • Potassium fluoride • improves gypsum surface

  17. Manipulation • Weigh powder • Powder added to water • rubber bowl • vacuum mixer • Mixed for 45 sec to 1 min • Place tray • Remove 2 to 3 minutes • After gelation Caswell JADA 1986

  18. Advantages Disadvantages • Inexpensive • Easy to use • Hydrophilic • displace moisture, blood, fluids • Tears easily • Dimensionally unstable • immediate pour • single cast • Lower detail reproduction • unacceptable for fixed prosthesis • High permanent deformation • Difficult to disinfect

  19. Impression compound • Impression composition • Modeling plastic • -cakes, discs • -sticks

  20. Impression compound • Properties • -inelastic/rigid • -thermoplastic • Manipultion ---- • -water bath ( hot water approx. 65oC) • -knead under water • -spread on a tray • -no crease • -CD preliminary impression

  21. Zinc oxide eugenolipas • -two paste system • -chemical reaction • -inelastic • -impression of edentulous arches

  22. Uses • To make impression of edentulous mouth • As a surgical dressing • Bite registration paste • Temprary relining material for dentures

  23. Composition • Tube 1- • Zinc oxide 87 % • Fixed vegetable or mineral oil 13 % • Tube no. 2 • Oil of cloves or eugenol 12% • Gum or polymerized rosin 50% • Lanolin 20% • Resinous balsam 10 % • Accelerator solution ( Ca Cl2 ) and colour 5 %

  24. References • Craig’s Restorative Dental Materials 13th edition by Ronald L. Sakaguchi and John M. Powers. • Dental Materials and Their Selection - 3rd edition by William J. O'Brien • Philip’s science of dental materials, 11th edition by Kenneth J. Anusavice.

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